Various types of nonwoven fabrics are produced by thermally bonding textile strands made from thermoplastic resins. Thermally bonded nonwoven fabrics of this type are used, for example, in disposable diapers, catamenial products, wipes, surgical drapes, clothing, carpets, wall coverings, house wrap, upholstery and packaging, to name but a few applications.
Many of the above-noted types of nonwoven fabrics may be produced by the well known spunbonding process in which a thermoplastic polymer is extruded through a spinneret to form a multiplicity of continuous filaments, and the filaments of molten polymer are solidified and then drawn or attenuated, typically by a high velocity fluid, and then randomly deposited on a collection surface, such as a moving belt, to form a web. The filaments are then bonded to give the web coherency and strength. The bonding may be achieved by passing heated air, steam or other gas through the web, or by direct application of heat and pressure, such as through the use of heated calender rolls.
U.S. Pat. Nos. 4,070,218 and 4,668,566 illustrate a spunbonding process wherein calender rolls are used to thermally bond a spunbonded web. As shown, after the web is formed on the endless forming belt, it is removed from the belt and directed into the nip of a heated calender. The web passes unsupported from the forming belt to the calender, and is thus subjected to tension in this unsupported span. U.S. Pat. No. 4,668,566 shows the use of compaction rolls on the forming belt for slightly compacting the filaments to improve the integrity of the unbonded web prior to drawing the web in an unsupported condition. However, because of the tension which is applied to the web in the unsupported span, there remains the possibility for stretching, necking-down, or even breakage of the web in this area.
With the foregoing in mind, it is an object of the present invention to overcome the limitations of the prior apparatus and methods for thermally bonding a textile web with calender rolls.
A further object of the invention is to provide a method and apparatus that allows for operation at a high throughput while reducing the likelihood of necking down or breaking the web and associated yield losses.